Aircraft propeller speed controller



A. P. DINSMORE ET AL AIRCRAFT PROPELLER SPEED CONTROLLER Feb. 16, `19548 Sheets-Sheet 1 Filed May 24. 1949 Feb. 16, 1954 A. P. DlNsMoRE ET'ALAIRCRAFT PRORELLER SPEED CONTROLLER 8 Shee ts-Sheet 2 Filed May 24. 1949COORD/NT/NG MECH/VISM TTRNEYS CTRNIC GOVERNOR Feb. 16, 1954- A. P.DlNsMoRE ET AL AIRCRAFT PROPELLER SPEED CONTROLLER File May 24. 1949 8Sheets-Sheet 3 Feb 16, T954 -A. P. DlNsMoRE ET AL 2,669,1312

AIRCRAFT PROPELLER SPEED CONTROLLER Filed May 24, l1949 `8 Sheets-Sheet4 A. P. DINSMORE ET AL AIRCRAFT PROPELLER SPEED CONTROLLER Feb. 16, 1954Filed May 24. 1949 8 Sheets-Sheet ...-MNAJEJT WR sin.

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Feb. 16, 1954 A. P. DINsMoRE ETAL 2,669,312

AIRCRAFT PROPELLER SPEED CONTROLLER Filed May 24, 1949 's sheets-sheet eK OFFSPEED f INVENTORS 5"' CWM #vw/1W Arron/vs Ys Feb. 16, 1954 A. P.DlNsMoRE ETAL AIRCRAFT PROPELLER SPEED CONTROLLER 8 sheets-sheet FiledMay 24, 1949 li. fffilflll,

TTR/VEYS Feb. 16, 1 954 A. P. DlNsMoRE ET AL 2,669,312

AIRCRAFT PROPELLER SPEED CONTROLLER Filed May 24, 1949 8 Sheets-Sheet 8A'rToR/vfxs Patented Feb. 16, 1954 2,669,312 AIRCRAFT PROPELLER SPEEDCONTROLLER Albert P. Dinsmore and R ton, James W. Light, Geyer, Dayton,and Joseph C. Whitmer, Bradford, Ohio, assignors to General MotorsCorporation, Detroit, Mich obert C. Treseder, Day- Greenville, Howard M.

., a corporation of Dela- Application May Z4, 1949, Serial N o. 94,98429 Claims. V(Cl. 17o-160.17)

The present invention relates to mechanism for controlling the speed ofa prime mover. More particularly, it relates to mechanism forcontrolling the pitch oi a propeller driven by a prime mover so as tomaintain the rotational velocity of the prime movers at a selectedvalue. The term prime mover is here used in its broadest scope and isintended to refer to engine, motor, or other power plant deviceincluding turbines, Whose speed control is themore critical and hencethe objective of this invention.

In aircraft installations Where the prime movers driving the propellersare gas turbines the controls used must be both vprecise and sensitive,in fact the controls, if they provide the proper governing action, mustprovide precise speed settings; they must provide instantaneous control;they must be sensitive to accelerations and decelerations as well asoli-speeds; and it is desirable that they provide a means forsynchronizing the several units of a multi-turbine installation. Thosenecessities obtain because of the characteristics of turbine powerplants in general, and must take into account that turbines haverelatively large rotational inertias compared with reciprocating enginesof the same power output; that they have smaller allowable offspeeds dueto the very small safety margins existing in-highly heated,centrifugally loaded turbine blades; that a minimum starting torque mustbe available because the turbines do not become self-sustaining untilabout 50% of their maximum rated speed has been reached; and

that the turbines, when coupled with dual propellers, in multipleinstallations, necessitate much more closely matched speeds than dosingle rotation propellers for synchronization. A satisfactorycontrolling mechanism then must be able to:

l. Set or select speeds of turbine-propellervoperation;

' to provide electro-hydraulic variable pitch pro- 2. Govern and holdthevset or selected speed under normal conditions of operation; and

V3. Synchronize multiple unit installations.V

It is therefore an object of the present invention to provide a controlmechanism which Will detect minute off-speed conditions and effectreturn to the desired speed accurately.

It is another object of the present invention to provide apparatus whichwill continuously regulate and control the speedof a prime mover over apredetermined range of rotational velocities.

It is another object vof the present invention to provideL controlapparatus for rotating ma-i 'l chinery which is both sensitive and fastin order to minimize both over-speed and under-speed conditions.

It is also an object of the present invention i to provide rotatingequipment control apparatus to provide control apparatus that can beeasily adapted for operation with any number of similar units.

It is another object of the present invention s; to provide controlapparatus with combined provision for governing speeds to approximatelya predetermined rotational velocity and having means for correctingslight olf-speeds of rotary members to the exact predetermined speed.

Another object of the present invention is to provide governingapparatus :whereby closely governed operation of rotational members withrespect to a, reference speed may be accomplished. It is another objectof the present invention to provide dual control for propeller pitchactuation, one of the controls to govern when the propeller is off-speeda large amount, and the other control to govern when the oi -speed isonly slight.V

Another object of the present invention is to 'provide control apparatusof the electro-hydraulic type [for variable pitch propellers, suchapparatus adapted to supplement hydraulic governing mechanism for minuteadjustment of the propeller pitch to obtain a predetermined rotationalvelocity and for sensing acceleration and deceleration and correctingthis change in rotational velocity in such a way as to prevent hunting.

It is another object of the present invention peller controlledapparatus adapted to supplement or replace hydraulic governing mechanismfor adjustment o-f propeller pitch, said electrohydraulic apparatusbeing capable of sensing rate of change of rotational velocity andcompensate therefore to prevent hunting.

Another object of the present invention is to provide control apparatuswhereby the speed of.`

rotary members may be regulated by the adjustment of a direct currentpotential. I

It is another object of the present invention g to 'provide controlapparatus for propeller pitch adjusting hydraulic mechanisms wherebypulses, of fluid under pressure are alternately applied to-v motor'316is connected to shaft |55 through a suitable gear reduction mechanism382. The movementl of this shaft |55 rebalances the bridge circuit339-342 by adjusting the contact 351 so that it again matches theposition of the contact 338. Movement of this shaft also adjusts speedcontrol potentiometer |39 and oscillator frequency control potentiometer213 while resetting the automatic speed control governor 402. The powerplant 434 is regulated to approximate speed by the propeller governorcontrol 482 and.

is directly connected to a three-phase alternator I5 which generates asignal proportional in both amplitude and frequency to the speed of thepower plant. One phase ofthe output signal of the alternator I5 followstwo paths, one directlyleading to the circuit |20, by cables |6b and|5c, and the other by cable |6a through the manual speed control |39 tocircuit |38. A D. C. voltage from rectifier-lilter circuit |20 islimited by a voltage regulator |32 and is fed into one side of a bridgecircuit |31 to act as a reference voltage for ne speed control. A D. C.voltage from rectifier-filter circuit |38I is set by the manual speedcontrol |39 and is fed through the automatic speed control |49 toy theopposite side of the bridge circuit as a D. C. control voltage varyingas a function of power plant speed for comparison with the referencevoltage from circuit |28. The circuit |23 is also fed into an anti-huntcircuit 4|2 to generate arate signal which, in conjunction with theerror signal from the bridge |31, is impressed as bias upon amulti-vibrator in unit |69 where proportional pulses are formed, ampliedby a buffer, and a power stage for energizing suitable relays 534', 54|,controlling a solenoid valve I4 operatively connected into the controlof the hydraulic regulator 6.

Fig. 2 is a schematic diagram showing certain of the linkageincorporated in the present invention. Each of the propellers I has aplurality of blades 5, the pitch of which can be adjusted by means ofhydraulic regulator 6. This regulator is controlled for initial speedsetting by a mechanical linkage 1 and cables 8 from the actuator unit482. Each of the pilot control levers 9 adjust an associatedcoordinating mechanism 430 which controls the amount of fuel fed intothe power plant as well as controlling its associated actuator unit 402.Each actuator unit y controls its corresponding electronic governor |2,

which governor is connected to the solenoid operated hydraulic valve I4by means of an electrical cable I3 having conductors 235, 236 and 231.This solenoid valve |4 is hydraulically connected to the regulator 6 forthe propellerhub. The engine driven alternator I5 provides an inputsignal to the electronic governor |2 through electrical cable l5. Thiselectronic governor if desired may be locked in step with othergovernors through electrical cable |8 for synchronizing a plurality ofpower plants.

Fig. 3 shows in greater detail, certain of the mechanical and electricallinkages schematically shown in Fig. 2. Referring to this gure, it willbe noted that the pilot control lever 9 is connected to a coordinatingmechanism 460 by means or cable 43|, and therein drives a cam 336. Thiscam has a proper contour so that its rotation, together with the linkage331, gives proper movement of the contact 338 of potentiometer 339 toproduce desired unbalanced signals in the control bridge circuit. Underconditions of bridge unbalance,- a1signal appears between theconducg 6tors 352and356 of magnitude and polarity which are direct functions ofthe magnitude and direction of mismatch between the movable vcontacts338 and 351. This signal is produced due to the unbalanced D. C. bridgecircuit associated with the power source 383. Under one condition ofunbalance of the bridge circuit, for example, adjusting the power plantfor higher speed,v a current in one direction is produced through therelay coil 353 to closecontacts 359 and 36|. Under opposite conditionsof unbalance, namely, adjusting the power plant for lower speed, currenthows lin the reverse direction through the coil 353, thus causing theclosing of contacts 36o-362. The field magnetic iiux of core 354 isreversednunder conditions of reversal of currentin the coil 353 :andthereby reverses the direction of rotation of the polarized armaturecoil 428, carryingthe movable contacts 359 and 360 of the polarizedrelay. The closing of contacts 359- or contacts 368-362 energizes relaycoil 365 or 366, respectively. The coil 365 is energized from powersource V383 through conductors 343, 358, 363 and 361 to ground. Theenergization of the coil 365 produces a magnetic ilux in the core 348 toclose the contacts 341-316 and thereby close a circuit from conductor343 through conductors 346, 312 to eld coil 314 of the motor 316. Thiscauses energization of the motor so that the armature 38| through gearbox 382. drives the shaft in such direction as to decrease the propellerpitch.i This shaft also drives the'contact 351 so as vto rebalance thebridge. Under conditions of overspeedwhen the contacts 360-362 areclosed, a circuit is completed through the relay coil 366 from powersource 383, conductors 343, 358, 364 and 368 to ground 389. Under theseconditions, contacts 350, 31| Vclose completing a circuit from powersource 383 through conductors 343, 349, 313, eld coil 315 of the motor316, conductor 311,'brush 318, armature 38|, brush 319 to ground 380.The armature 38|, under these conditions, rotates in the oppositedirection to that mentioned above to cause decrease in speed of thepower plant and to rebalance the bridge circuit including thepotentiometer 342. It may be seen from inspection of this iigure thatthe shaft |55 also drives the contact 211 of the automatic speed controlfrequency potentiometer 213 to vary the frequency of oscillator 243.This shaft simultaneously adjusts the movable contact |43 of the manualspeed control potentiometer |39. The shaft |55 also drives theY control482, which acting through the cable 6 and linkage 1, moves the rack 580to rotate a screw shaft 85 through pinion 502 to adjust a speedsensitive valve 35, as will be described with reference to Fig.. 8. Theactuator mechanism of Fig. 3 keeps the two governing systemssubstantiallyin step by coincident adjustment of the two potentiometers|39 and 213 forA the electronic governor, and the rack 530 of thehydraulic governor so that the coaction of twofrelated governing systemscovers the entire range of desirable'pitch shift movement.

Preliminary to detailed description of the electronic governor that isable to (1) set av precise speed of turbine operation; (2) govern andhold the selected speed under normal conditions; and (3) may be requiredto synchronize multiple unit installations, it should be understood thatthe electronic governor, in addition to having simpleproportionalsensitivity, also has rate and integral sensitivity whichmay be designated as K1. K2. ,and respectively. K1 is the propor.y

` vibrator circuit. The point 'pear as a grid bias on the respect topoint |56 of plus one-quarter (-l-A) volt and point |53 assumes apotential of minus one-quarter 1/4) volt. If the speed error is twice asgreat and there is an increase of two (2) volts at |50 and |52 then apotential of one (l) volt will appear across |51 and |58, plus one-half(-1-1/2) Volt at |51 and minus one-half 1/2) volt at |58. Thus, equalvoltages of opposite polarity appear at the bridge output terminals |51and 53 which, in a governing sense, are a direct function of speederror.

Theresistor network across the points |35 and `.|36, including theresistors |00, ISI and |82 together with the resistors 522 and 523 ofthe bridge |31, forms another bridge circuit. If the value of theresistor |80 is equal to the Value of the resistors |9| and |52combined, the potential of the point |04 is equal to that of the point|56. This resistor |80, however, be adjusted for purposes of calibrationto provide small potential differences to exist between points |04 and-|56 as may be required for adjustment of. the multi- |84 of the resistornetwork is connected by means of conductor |81 and resistor |33 to thecathodes of both the tubes |9| and |52 of a multi-vibrator circuit. Thepoint |58 is connected to the grid of the tube |9| by means of conductor|60, resistance |62, conductor |64 and resistors |15 and |14. Theterminal |51 is connected to the grid of the tube |92 by means ofconductor |59, resistor |6I, conductor |63 and resistors 11, |10.Attenuator networks comprising resistors |62 and 90| on the one hand,

and resistors |6| and 902 on the other hand, are inserted as fixedsensitivity adjustments. By means of these networks, that part of thepotential difference between the points l|58 and |56 which appearsacross resistor 90|, will appear as a grid bias on the tube |9|,'whilethat part of the potential difference between the points |51 and |56which appears across resistor 902, will aptube 92. Thus, the potentialsappearing across the output terminals |51-|53 of the .bridge circuit,form a means of control of the multi-vibrator circuit.

' The multi-vibrator circuit is of conventional design using triodetubes 9| and |92. A modication of the usual multi-vibrator circuit isprovided for adjusting the biases on the tubes 9| and |92 to control thesymmetry of the multivibrator output signal. cludes applying as biasvoltages, the potentials which are developed across resistors 90| and902, connected to the output terminals of the bridge |31. When the biasvoltages applied to the grids of these two tubes are zero, the circuitis a standard multi-vibrator circuit in which the wave form of theoutput signal is symmetrical and approximately square, and the pulseratio may be considered as unity or of 50:50 ratio. If, however, thebias on the grid of one of the tubes becomes slightly negative while thebias on the grid of the other tube becomes slightly positive, theconduction times of the two tubes are not equal and the signal wave formis unsymmetrical with the pulse ratio in other than 50:50 ratio (e. g.60:40). This action of course may be reversed by reversing the relationof the bias voltages.

With respect to this variation of bias, it should be obvious that theoli-speed condition, as represented by the application of zero biassignals from the bridge outputterminals |51 and |58 upon the tubes 19|.and I 92, will effect a 50:50 pulse ratio. An over-speed-condition willpro- This modication ,in-

lays have potential at point |51 on bridge deliver a positive bias tomulti- In a similar manner, the tube 9| will receive a negative biasfrom point |58. 'I'hese bias voltages make the conduction time of tube9| shorter, and that of tube I 92 longer, thus producing a pulse ratioother than 50:50, for example, 40:60. Continuously increasingover-speeds will produce ratios of 30:70, 20:80, etc., until tube |92becomes continuously conducting while tube |9| remains inactive andpulsing ceases. On the other hand, an underspeed conduction of the powerplant will effect a reversal of the action of tubes |9| and |92producing pulse ratios 60:40, 70:30, etc., resulting finally in tube |9|becoming continuously conducting and tube I 92 becoming inactive.

The'power level of the signals at the plates of the multi-vibrator tubesis insufficient to operate control devices capable of changing the speedof the power plant; for instance, as here applied, to the change ofblade pitch of the propeller driven by the turbine. In the installationillustrated, a direct coupled amplier system including buiTer tubes 22|and 222 and power tubes 230 and 23| is used. The power tube outputsignals are impressed on the leads 235 and 236 to energize one or theother of relays generally indicated at 534 and 54|, respectively.'I'hese rewindings 536 and 538, respectively, serially connected acrossthe leads 235 and 236 with a connection at mid-point to a power line 5|1connected with the positive side of the power supply 242. Contactelement 540 connects with solenoid winding 62 and contact element 542connects with solenoid winding 63. 'The windings 62 and 63 have `acommon ground connection 64. Cooperating with the contact elements 540and 542 are armatures 530 and 532 joined with a common lead at point 53|making connection with an electric power source suitable for theactuation of solenoid valve |4.

Any off-speed of the turbine therefore manifests itself inproportionately diiering electrical pulses impressed upon the conductors235 and 233 and thereafter transmitted by the relays 534 and 54|,respectively, `to the solenoid windings 62 and 63. This eiects suchmovement of the valve I4 as to apply corrections (of the nature shown ingraphs Ay to D of Fig. 6) to theY blade servomotor in the hydraulicregulator 6. This will be described in detail with respect to Fig. 8.

During on-speed conditions, the solenoid 4 is given equal and alternatepulses on the windings 62 and 63 so that the hydraulic pulses in controlpassages 53 and 54 are equal. Such energization causes the servomechanism to maintain the blade 5 in a substantially constant position.During a condition of power plant oispeed, the solenoid actuated valvevI4 is given a series of alternating pulses ofV unequal pulse duration.For example, if the engine or turbine is experiencing an over-speed, thesolenoid actuated valve will oscillate under such conditions as to openthe control passage 54 for a longer duration of time than it does thecontrol passage 53. The blade servomotor, under such conditions, will beactuated in a direction to increase the propeller blade pitch angle andthereby reduce and correct the power plant speed. For conditions ofpower plant under-speed, the relationship of pulse length and thereforeunequal opening of the passages 53 and 54 will be reversed and acorresponding decrease of propeller blade angle will be made, resultingin Van induce a positive |31 and in turn, vibrator tube |92.

z crease in power :plant s being controlled; is rofi-speed .a large.amountjthe ,magnitude of :the voltage". from 1 theibridge f circuitI31will be suchfas :tocausez'onef-of` thefinulti- :vibrator tubes tozbeicutisofra-ndiv theffother-` tube x .to conduct constantly.

s change oi propeller:

maximum correction: of =powerfplantftspeed- 1 Vners 555 and`-556` andresistor.,554

...across the yloadcircuit to .minimize arcing-of the s contactsv 56e#and S56 I automaticallyenergized -when-fpropeller featherof thetransormernl. M3, of this, potentiometer ,is..drivenby the shaft causehunting conditions to,.o,ccur,which.A

eed. 'i rif; theapowerr; plant This-:results in continuous current .flowVthroughiifone. Aofi the. conductors i235 or 23e with: itsVcorresponding@relay operated to energize :one `of the :windings:-oimsolenoid actuated valve'diacontinuously. vThis maintains eitherpassage. r53 `:or 54 open to give fullrateof pitch; and thereby it eectsAn arc suppression :circuit fconsistingzoffrectiisl provided the'relaysf'534randf4lconditions' of opswitching contacts-fof It isdesirable. 1under certain eration, forexarnple, duringpropellerl-feathering or lpropeller' operation in the negative-.pitchrange, to disahleithaeiectivefoperation of I the solenoid yvalves ILeland i forithat purpose a fdisconnect relay :is provided" for'operating Isivitch theI relay 1 coil L5552 being ing,A or `any:conditioniof operation fotherz than normal governing, isffselected.

vIt is necessary A.during on-speedi conditions that thevoltageswappearing across the rtwdpairsof iinputztermin'als ofifbridgenetwork JIS'I-.be equal.

In order towaccomplishithiszcondition, .an attenuationnetwork-eisprovided-fsothe speed responsive voltage across'gi llzandf Ii2= of f the Vbridge I3? -rnay be madei'thefsame #at-@thefpreselectedAspeed as ther-'reference voltage-at the l:points 2135- I 36. NThe"attenuation .necessary-ris' accomplished by means of tentiometerlf39-and a; `manual speed control poal series oonne'ctedfxed rel sistor|40.

yReferring tof-Fig.V Llv-ofithe drawings, `thesarne phase or the'alternator-limpressed upon"the winding IIS .is impressed across thepotentiometer IBS, and` resistor "M0 to`` furnish the. desired voltageamplitude across. the primary 505 .'The.movable contact AIE lto'adjustthe ,proportionoffthe A. @voltage from the ;alternator-.-I 5tube-.impressed acrossfthe primary 508. This voltage.: determinesfthevA.C.

input to thelrectifieri-lter. vcircuit -I38..and thereby theD.fCrfv-oltage,l to :zbesappliedi-to ther-points ldangerous speedoscillations. l.An acceleration sensitivel control. or some form. of.,anticipatory. contr-.ol must be incorporated toiprovidethe dampingrequired `withthe high rates .of-.K1 control needed for fast governoraction. Suchaccelerationsen- `stive control has earlier "been:.dened=..as;.-K2

control, a proportional-ity between rate .of pitch change -andfratefofchange of turbine'` speed.

12 1K2'. control *In order to yprovide av governorthat'willbesensitive/to accelerations and decelerations -o YVof the power plant andconnection to '|84 `through i431.

the turbine -orfotherf-power plant, a control is vprovided thatsensesKrate of change lof speed responds in terms'oi propeller pitch changes.This control includes a circuit which'converts accelerations ordecelerations of thef'power plant speedv intopositive or -'negative`D.Cnbias potentials, the labsolute value of which areinstantaneously-proportional to, andiinpropertrelation or sign to,

the accelerations or decelerations 'of the'power plant speed. tronicgovernor 4In the heretofore described elec- "for `K1 control, there are'two resistors "504 andt, in series with'the voltage Iregulator tube|32, between conductors itt and Electrically connected'across theseresistors are-two circuits vconsisting of capacitor I'Gl andresistor"002011 the one hand; and; capacitor I-Si''and resistor-'$10! on theother handyresistors-'l andl 902 having a common The Values of thesecapacitors and' resistors'aresuch that the circuits act as electricaldifferentiatingxcircuits and provide equal voltages ofiopposite'polarityacross resistorsSI and: 002 'whichvary `as the first differential :ofthevoltagechanges appearplant accelerations".` and decelerations. `voltagesignals areapplied to the' multi-vibrator Y*1nV combination 'with ine"between conductors and'I'3I. Since this y latter voltage'is'directly'proportionalto speed, the voltages across resistors' '90|'Land'. Bt? 'are therefore proportional to rate of'changeof speed,reversing their polarities respectivelyior power These tubes asvcontrotbiasee and. 'are v`'connected so that acceleration of `powerplant'speed'tends to `cause an increase in propeller, blade angle. Lrhese voltages `are 'applied to the `multi-vibrator grids the'voltagesfrom. points 'I 5E?.V and .I 51 of 'bridge |131 ,"and the algebraic sums:of th'esegtwo voltages are the instantaneous multifvibratorrbiasvoltages, and y.therefore determine described, effects V 'speed which'isa vcombination.of'a simpleK1, or

i potentiometer 1I t9. ithefzpotential appearng-.betweenfthe' points.itt V and i152:atftheiinputfof-gtheibridge I3'l. Theos- 'The governingsystem so far a. control V"of the. .power plant the pulse` ratio.

speed .sensitivezcontrolfaugmented.by a K2, or rate'sensitiye control..'l-Ioweverjthe control impressedupon the lines IBS `,and It is .furtheraugment'edbyan:automatic Yspeed control applied throughpotentiorneterM9, and which has ,been hereinbefore'referred to as K3 sensitivity.

control "'Thevpresent'invention contains an automatic 1speedcontrolicircuit which is'irequency sensitive, correcting*fory errors;yin the `voltage Asensitive K1 governor. (i0

sp eed. control,- fand f also permits 1 synchronization rof turbines or:other."powerA plants. This K3 conktrol:istanother governor-systemandefiects its inrrluence byrmodiiying thek Kr `control vthrough ad-"rnent- .is :madefat 7a'frate,ifproportional lto :the fre- A fluency`difference between' theo'utput of the alter- 'nator 'i5 and YThissystemreerred to 'as K3 control, beine '-ireqiiency-sensitiveY affords very'precise justznent 'ori-the*4 potentiometer i129. f' '.Tltiisadjustthat-oiqsome preselected alternating frequency signal source.Figs. 4 and 5 show this v automatic "frequency-control system 'asincluding an :oscillatorv unit 24o; aiphase discrirriinatingr unit 2:4 Ial synchronousmotor Mie for adjusting V.This potentiometer frnodiiiescillator 240 is an adjustable reference frequency source which impressesthe reference frequency into a discriminator 24| for comparison with thethree-phase alternating signal. 'Ihe output of this discriminatorcircuit energizes the windings 308, 309 and 3|!) of the three-phasesynchronous motor |54 to effect adjustment of the potentiometer |4Q.

The oscillator 24U is a resistance-capacity tuned oscillator ofconventional design. Frequency adjustment is accomplished by variationof the manual speed control potentiometer 213 incorporated in the tunedgrid circuit of the first stage. The plate supply voltage oi thisoscillator is obtained by conductors e3@ and elli from the power supplygenerally indicated at 2132 in Fig. 5. By proper selection of thecomponents of the oscillator, and through adjustments of the resistors21| and 276, a frequency range may be obtained that is identical withthe frequency range of the alternator when operated in the normalgoverning range I" the power plant-propeller combination. A scheduledoscillator frequency is simultaneously set for any selected speedsetting, since the frequency determining adjustment |49 is operated byshaft |55 of the manual speed control servo system. The oscillator maybe synchronized with other oscillators or" similar design for thepurpose oiV synchronizing multi-power plant installations, byintroducing a synchronizing signal across the resistor 23|, fromVsimilar positions on similar oscillators as indicated by 4D6, 496 andim of Fig. 5.

There is a gating circuit including tube 98d in the oscillator unit 240;In this circuit, the plate load resistor 95|) is connected between plate963 and ground 255, while the cathode 95| is maintained at a negativepotential by power supply 2442 'through lead 552. The grid c62 iscoupled with the oscillator output through capacitor Slt and has itsplate 953 connected over the line 43S to the grid circuits of the tubesill, 3 I5 and 3 i6 of the discriminator 24|, through resistors 3M, 305and 33t, respectively. The discriminator tubes 3|4, 315 and 3|6 havetheir grids connected through a yseries resistor network 25?, 258, 259each to an individual phase of the alternator I over leads 8, and H6,respectively.

The tube S69 acts as an electronic switch or gate operating at theoscillator frequency, and thereby controls conduction times of thediscrimnator tubes 3|4, SI5 and SIS, switching them off and on at theoscillator rate by alternately biasing all grids beyond plate currentcutoi. The plates 3| 3|2 and 3|3 of the respective discriminator tubesare connected, respectively, with the angularly'disposed eld windings3513, 389 and 3|!) of the synchronous motor |52, while acommonconnection of the eld windings is made by 5I8 and Sit to the positiveside of the power supply 242. Each motor winding 3&6, 359 and 3 il isshunted by a condenser 3H, 3|3 and 3|9, respectively, that averages orintegrates the current owing in the respective plate circuit when thetubes 3m, 3|5 and 3|6 become conductive.

'I'he operation of the discriminator- 24| is indicated by Figures 9, l0,l1 and l2 where the a1- ternator and oscillator signals are representedfor illustrative purposes only as having a square wave form. The dottedlines GP indicate ground potential, which is equivalent to cathodepotential of the discriminator tubes.r The alternator signal (A) issymmetrical about ground potential, swinging alternately positive (Ap)and then negative'An) with respect thereto. The oscillator j 14 signal(O) is always negative with respect to ground potential, due to the factthat on half cycles, when no current flows in gating tube 96%, there isno potential drop across resistor 950, the line 38 to the discriminatorgrid circuits remaining at ground potential (Op) and, on the other halfcycles when current iows in gating tube S65, there results a potentialdrop across resistor 956 that is negative, the line 438 becomingnegative (On) with respect to ground.

The amplitudes of the two signals are approximately equal, but the peakvoltage of the oscillator signal with respect to ground is approximatelytwice the peak voltage of the alternator signal with respect to groundon either half cycle and the peak values of both of these voltages onnegative half cycles are in excess of the cutoff bias value of thediscriminator tubes 3|4, SI5 and 3|6.

Each negative half cycle of the oscillator signal (On) holds alldiscriminator tube plate currents cut off. Hence the gate tube 960 andits associated circuit acts as an electronic switch operating at theoscillator frequency and controlling the discriminator. The alternatorsignal, though mixed in the grid circuits of the discriminator, with theoscillator signal, acts as an independent grid signal.

When there is a frequency difference between the alternator signal andthe oscillator signal, the relative phase angle is constantly changingand phase rotation results in a direction depending upon the sign of thedifference, becoming zero Where they are in phase, Fig. 9, and rotatingthrough 180 degrees and around again through zero. The rate of phaserotation, or beat frequency, is equal to the diierence in frequencybetween the two signals.

In Figure 9, the alternator and oscillator signal frequencies are equaland in zero phase relation with each other. Plate current (PC) is cutoff for exactly 180 electrical degrees (PCO) on alternate half cycles,while both grid signals are negative on one-half cycle as at (An) and(On) and f current is caused to now on the remaining half cycles (PC) orwhen the oscillator signal voltage is zero (Og) and the alternatorsignal voltage is positive (Ap). Plate current flows half the time andthe average plate current is one-half the peak current value.

In Figure 10 the two equal signal frequencies are represented in phasequadrature, or the alternator cycles A', A, etc., are out of phase by 90degrees with respect to the oscillator cycles O. O", etc., as indicatedby t. Here plate current is again cut off (PCO) during the half cycleswhile the oscillator signal is negative (On) and remains cut off for anadditional (t") due to vthe presence of the negative half cycles (An) ofthe alternator signal and is caused to now over the remaining 9D degrees(tm) of each cycle or while Vthe oscillator signal is zero and thealternator signal is positive. In this case, plate currentlows for only90 electrical degrees of each cycle and the average lplate current isone-fourth the peak value.

AIn Figure 11, the two signals (A and O) are represented-in phaseopposition and since one or the other of the signals (An or On) isalways negative, plate current (PCo") remains cut on during the entirecycle, and the average plate current is zero.

If kthe Yindividual plate current pulses of the discriminatortubes areaveraged in a circuit whose time constant is several times the periodphrase, asin Figure mum; whereas at time T',

f esili-angina'rl-y cij the motor, and 'produces afrotat-irlgfield"effecting rotation of the motor armature.

feffeiuier cfluieesifgalfrecuencias this average relate-cu einemvery1wiutchangesiin thereatire phase-angle--betweenthe two v signals.When Tfafdiiierence-'exists between the irequencies oi the two'signais,the yresulting"phase rotation at the f' difierence frequency produces anaverage plate current cycling throughmaximaandininima at Y 4thediiierence 'frequency `In lsuch dynamic operation the relative phaserotation of the twosignals'-passeslthrough all of "theistatic conditionsillustrated in vFigures 9, l 'and ll--and a sinusoidal -cycling of theaverage plate` current occursas illustrated in Figure l2. At time T, thetwo grid signals-A and O are in Y l the signals are 189 cut'oi phase`andpiate' current minimum, as

Yin 1Eigure ll.

It is to be understood that, while Figure l2 is n a-plot theact-ion "inoneifof the discriniinator tubes yasimilar# action takesplace ineach ofthe "tub l-'plateS-' Ei l ,1 3 i2 endl-3 i3 jtubesare'connectedtotnetlireepliase-iield wind- .mg

, 3i-E and 3' i''inFigure-. The respective of these v'discri-minat'orSill, respectively, of Aa vconventionalthree#phase-'motor#i'. vThecapacitors The armature shaft i'fof the motor as f shown' in'iigs. ilandfis# connected 'to 'the movable f arm `oi' `Vpotentiometer fi '39,rlhis resistance,A Y"as previously mentioned the D A yseries element in*circuit *of the idgef input yterminals c2, defined as f the-#automaticfspeed control. Ope ticzr ofthe circuitis suoli tllatfforl example,

creases-the potential 'across the bridge Band thereby causes anincrease"i opellerlblad tch y"ang-le to reduce the speed. .1 the discrlminatorunit Zeil f electronically compares the frequency 'of the prime rnoverlrdriven three# e vait natori5'to thatof the oscillatcrfiic", translatesang/difference in frequency due itc-speed Yerror into tn-adjustment cipotentiometer lie-'in proper-direction to ene-ct a coiiectionoi thespeed-error. Y

` Apower `supply-2&2 in Fig. 5 of conventional `design is used toenergize the oscillator, the discriminator and the `motor mentionedabove. "This power supply may be 'energized lfrom the rusual aircraft or`other conventional y'power sources. -As' specifically illustrated,it'isenergized v"from a transformer 245 Yhaving aprimary '51*9 'andsecondary 543. :This transformer also has `secondaries545, '56'fand 541"to fsupply heater gating tube, multi-vibrator, and Aoscillatordiscriminator, `sections respectively. The center 'tapped'secondaryisfsoarranged with a rec- 'tifier-lter circuit as toproduce a direct currentpositive potential on the conductor SI5 and a directcurrent'negativepotential on the conducltor 552.` One of the rectifier circuits includesfrectieis "24S- and"241" connected' from' thefnds of 9, and platecurrent `is maxi- 1 circuits throughl a 'by what is referred to as a "bythe oscillator 2MB, discriminator Edi, motor 'impressed upon theconductors liiand lee.

755| connected f'fromthe `:ends fof fthe" "secondary Mil-to theconductor 552. conductor. 552A YThe-voltage on the is-n'egativeDC.voltage 'filtered by 'capacitor 249, resistor 912 and capacitor ii andis used asa cathode'voltage supply for the gating tube'SS in' thevoscillator unit Elib. A D. C. positive lvoltage ltered by capacitor 2558is produced on the conductor SI5, and is used to energize'thesynchronous motor 151| through a iilter circuit including 'resistor @I0and capacitor 5| 4This conductor'also furnishes a plate voltage for theVoscillator 2 40 through a inter-including resistor S05-'and -capacitorSill, Aand is `a source of power for the solenoid valve and poweramplier iilter including resistor eed and capacitor 909. Resistors253fand 255i are bleeder resistors across the capacitors 248 and 2&9,respectively, in theD. C. power supply circuit.

Resistors'lil,` |S| and |32 form a network 'across the A'regulated inputto the terminals |35 and |36 of thebridge to provide proper potentialsfor Athe cathode and yplate circuits of the multivibrator section andits amplifiers. The conductor 5H furnishes positive potential fromtheconductor vSI5 to provide plate voltage for the power stage andenergization for the relays 532i and 5M and the solenoid windings '62and 53 of the control valve I4.

The several units and assemblies of the electronic governor thus poweredand connected provide apparatus for speed control of the power plantload combination to maintain precise speed operation. Manipulation ofthe pilots control member "9 while selecting af-particular `speed of.operation coincidentally controls potentiometers |39 andf'l and'alsothe hydraulic governor control 6.

A voltage is thereby set up in the circuit itil and a referencefrequency is produced in the oscillator 260 whereby the hydraulicregulator is maintained within the general propeller pitch range atwhich the propeller power plant combination is to operate. The bridgecircuit |31 provides what we herein refer to as a K1 control, bycomparing a reference voltage at its terminals |35 and |35 to a speedresponsive voltage provided by the circuit |38 at its terminals |56 and|52. This speed responsive voltage occurring at the terminals and |52 isprecisely adjusted K3 control provided |54, and associated mechanismoperating the potentiometer |59. rihe bridge circuit |37 thereforeacts'as a comparing and sensing mechanism at the same time and impressesupon the conductors |63 andlc a control voltage that contains both theK1 and K3 factors mentioned above. In order to prevent hunting, thevacceleration or anti-hunt circuit il l 2 provides an accel- 'erationresponsive voltage K2 which is added algebraically to the voltage abovementioned as being We now have impressed upon the conductors it@ and ltda multi-vibrator control voltage which cor. bines all three of the abovecontrols, namely, i521, K2 and K3 controls. The multi-vibrator circuitlis thereby caused to oscillate so as to provide an output pulse lengthratio containing these three control factors.

The action of solenoid actuated valve it iollows the individualmulti-vibrator pulses, responding Eto' all of Ythe control functionsapplied to the con- "ducto'rs |3fand |513. YThe oscillatorymovement o4"thesolenoid'valveappliespulses" of hydraulic of Figure 8 in the sameproportion as the pulse length ratio from the multi-vibrator, andtherefore, applies control forces to the'chanibers 5| and 52 which arethe combined effects of the con- Figure 6 illustrates this pulse'lengthratio under conditions of on'speed, slightly oiffspeedl greaterolf-speed and far off-speed by charts A; B, C and D, respectively.Thus,` under on-speed Vconditions, the ratio of negative pulsea'topositive pulse b is 50-50. Under olf-speed conditions, the ratio ofa to b is approximatelyA 30-70. Under larger oir-speed conditions, theration" to b" becomes 20-80. Under `conditions yof far offspeed, thevalve is held at one extreme position or under the continued flowposition 17"?.

The valve 4 is shown in Fig. 7. It comprises a body having a central'bore with enlargements |02 at each end. The bore |6| is fitted .with aporting sleeve |03 that has control ports 55 and 56 that communicatewith control passages 53 and 54.through annular'channels |06 and |01, inthe valve body. |90. Thevalve body also has a passage 2`4connected withan .annular channel and pressure supply. port |04. The solenoid windings62 and 63 are disposed each in one of. the enlargements |02 and rtheredisposed around pole pieces |08 and-m6,

respectively. Avalve rod ||0 has rigidly at- Vtached thereto coreelements 60 and 6| supported centrally of supporting sleeves ||3 by.resilient diaphragms .|||-||2.. The rod ||0 also has formed thereonspaced lands 51 and 58, respecu tively, that close ports 55 and 56 toiiuid flow f while the valve assembly vis in the central position;N Thewhole assembly isv such that inA the restgposition, the portsA 55 and 56are closedto fluid flow, yet electromagnetic;actuationzof theVcorel-.members will shift the valve stem ||0 so as to expose ports 55and 56 to hydraulic pressure applied through the passage 24. Forexample, Venergization ofthe winding 62 will move the-'valve member |0rto the right so that the port 56 will be exposed to pressure and theport 55 1'exposed to drain. Energization of the solenoid winding 63 willcause thevvalve member `||0.t`o

inoveg'A to the left thus exposing ythe port .55' to pressure and theport 56 to drain; fThus, ports 55 and 56 are connected to the bladepitch 'servomotor chambers 5| Vand 52. through lines 53'and i8 forfeathering or downfor negative pitch operation. When this valve is setas illustrated for governed pitch operation,k annuli or grooves 3| andV32'of a valve plunger 33 are exposed to the low pressure of the line`26,which pressure is also introduced to a groove 3a or a plunger 35 in thespeed sensitive valve 29. K y 1 The speed sensitive valve 2s alsoincludes a porting sleeve 35a embracing the valve plunger 35 and has aport 62. controlling the ow of iluid into av hydraulic line 36 leadingto a groove y31 ofthe selector valve plunger 33. The groove 31 permitscommunication between the passage 36 and a branch' f, g or n of apassage 38 to a. large servo chamber 35 of theservo actuated distributorvalve 21. vThe movement of a plunger 44 of this servo actuated valve isalso under control oi pressure introduced from a groove 32 of the valveplunger 33 through a branch f', g or n of ,a passage 4| to a chamber40.The chambers 39 and of the servo actuated distributor valve 21 .aretraversed by piston members 42 and 43, re-

54 as shown in Fig.r8. In "this manner the'solenoid valve effects itsblades. Y l The hydraulic apparatus capable of varying the propellerpitch is contained withinthe'regu-A- lator 6, and is self-operativeduring propeller v'control to the propeller Arotation to roughlycontrolthe propeller without any outside ilui'd connections. (Thisunit'lis graphically illustrated in Fig. 8 ofthe drawings where 20refers t0 a system pump` driven byrof tation of the propeller so as tocreate a source of iluid pressure in line 2|. The pressure in this lineis regulated by variable pressure control valve 22 and high pressurerelief valve 23, so that the pressure in line 24 isalways suiiicient'toefvfect any propeller pitch control called kfor by the governingmechanism. The line`24 'connects the high pressure witha pressurereducing valve 26, the solenoid operated valve A| 4, and a servoactuated distributor valve 21. A low pressure line y28 extends from thepressure reducingl valve 26 to a Speed sensitivev valve yunit 29, and toa selector valve 30. YAs illustrated in Fig. 8, the selector valve 30 isset for-:governed pitch operation but maybe moved by Vcam surface"90fleither up also to a piston 68 in. a

the piston 68 is always force and by a spring s pectively, which aresecured to the plunger 44 having valve porting lands 45 andk46coincident with ports 41 and 48. These last mentioned ports ycommunicatethrough passages 49 and 50 with chambers 5| and 52, respectively, of ablade `servomotor which controls the pitch of the prof peller blade 5.;The' blade servomotor is," also under control by the solenoid actuatedvalve I4 through passages 53 and 54 eiected by the control circuitshownin Figs. 4 and 5 giving the Ki, K2 and K3 control mentioned above. l Thecontrol passages 49 and 50 are also connected to a pair of passages' 64and 65,y respective- 1y, which communicate with opposite sides of 'ashuttle valve 66 that forms part of` the variable pressure control valve22 for regulating the pres'- sure potential of the system.' As pressureis applied to either passage 49 or 50 for moving of the blades 5 of thepropeller, that pressure will also be applied against one end or theother of the shuttle valve 66 to move it,` toY a position whereby thedistributedpres'sure may be applied chamber 61 of the pres- The oppositeside 69 of subject to pressure from thepump 20 through the line 2|. Thispiston 68 is urged radially outwardly by centrifugal j 10 that assistsVthe pressure in 61 and opposes the pressure in 10 so as to partiallyclose a port 1| in response to the combined vforce of the fluidpressure, spring force, and censure control valve 22.

`trifugal force. That meters the flow of Iiuid from the line 20 throughthe port 1| and passage 12 topa piston area 13 of the pump control valve25. Pressure againstthe piston area 13 opposes centrifugal force onrtheplunger and tends to open aport 14 to drain. It also opens a drain port15 for a delivery line 16 of an auxiliary pump 11 which is driven'during propeller rotation, If the flow exertedagainst the piston area 13is insufcient to open the relief ports 14 and 15, nuid flow from thepump 11 isdelivered through the .passage 16 and a'ball .check valve 18to augment trated in Fig. 8, this apparatus is shoi'vn inthe speedgoverned relationship under such conditions that there is no tendency onthe ypart of theservo system toeither ncreaseor decrease -the vpitch ofthe propeller blade. Should there be an'increase in speed overtheequilibriuni conditions here shown, the'valve ,element S5 willmoveoutwardly touncover port 8 2 in the sleeve 35a to establishnuidconnection between the line 2% andthe 'passage 36"`and" through thispassage',

'slref on thepiston vhead 42 in thech'amber.

Under conditions "of governed pitch operation, pressure fronfrtlrlevline 28 is also introduced into the lanib'er against vtheloyver' side ofthe vpiston headl #i3 through groove" 3 2 and passages `Mg 'andv ll IThel 1'piston l1ea'd i 42 'is' lrnuch' larger tha'n the piston Aheadvinland therefore under jcon ,'dition'g'of equal pressure inthechambers'BfQ and '5 0' the 'valve 'nieiriberll will' rnove downward vtocnneet the high; p ijessureline` 4 with the oo n- Ytrol'pa'ssage Efby uxnafslaing port 48. Hydraulic p ssure iorn line' 24 is thus introducedinto the vochan er SZtornove the blade '5 in such a cl' tionf'as creaseits pitch. Theincrease ofY pitli ofthe propeller blade increasesthe'load on the'rigyine turbine or other prime "rnover driving thepropellerndthus reducesthefangular'v locityfpf propeller 'lrotation. Theldovvnvrd moveient'of the? alvenemb'er 'de causes the relaiation" ofVpressure ona cam "member 83 allowing 'itto' `i`rio`ve towardthe right as'shovvnjin KFg.v'llfi'iflfi' "allot/s the porting sleeve"35aofthe 'valyemeinber 2 9 to rnove upwardly' thereby shift- 'ingthe port8-2fso thatitis Vagairrfnaskecl"byt he 'valve plunger" 35 tostop"anyf'iurtlfierflow of the lovvr s iire fluidtotheservooharnberit.

Sh uldthe propeller decrease inspeedso that than that `-de sired,

stresser-eti from' the Vcl'larnber 5 Vmay bef exhausted through f84.Under conditionswvhere fisrased so that the: port 41=a-nd chainber'iiare Vexposed tohigh pressure vfrornthe passage fthe 'p'ort* 48' is4-simultaneously nnnuasked` so' that I press're irom the *chamber '52 *maybe-v exhausted through the passage 50, port 48 and port B5 to mare se 29is again cut out of the drain. The 1ands'45'- and teef valve?? are 'considerahlyfnder thanftheports 41" l"`so" as to bear a relationoflpos'itive'overlap 'Thevalve Ihe speed'ran'ge'riaybe set'atariylesirlevel bythe -pilot upf'n oving Vthe hand'lever' (Figs, 2"an'd 3).r'nent/of this 'con'trol, "the cable connecti'nand linkagelf'ef'fectsthea'rcuate placement ofthe ring `member 500 (Figj'B), Whichby gear502and'screw adj usts'theposin tion of 4fulcnium lalong theleverjt. Theposi- 'tio'ri of the `fulfarfurnjI on the lever @il 'determines thevspring forces applied to the valve member If thepilot"'\vishe s"to'increase the speed ""tting at "which the'apparatus will` govern, 'hewill so "'actuate the-'lever Sth'at the viulcruifn 8i *'willfbe lmoved'tov/a1'' d thefright of thelever 3i), thereby giving'tlie spring 82agreater advantage-against "centrifugal'foree onrth'evalye rneinberl'.The spring force" ofv course 'inu'st be' over-Corne by centrifugalforcefto cause' actuation yof this f vali/e ymember to f a ne'vvequilibriurn`4 position. n'der these conditionsthevalvehierber 35 willreach equilibrium position ata higher 'centrifugal force and thereforehigher rotational'speed'than at its-'previous setting.

If the 'pilot f'wis'hes to-'redue A"the rotational speedof the power 'iplant; ll'ie rthani'pulates the ilever 9 so asto" rnove thefiulcrunil vtothe letlalong the leverllfor' away'from thevalve 35. This causes A'theSpring 1,82 'to 'have' less advantage throughthe 'lever 8 0 onltheya'l'vej niernber 35, hich'is balan edf-by less vn :entri'tugalforcejand `therefore, 'lessfrotational speed is 'f required' to reachanfeouilibriurn posit1`o1 'i, Movement of 'the fulcrurn 8l alongftheflever -80' determines the 'operating "condition f of *the vproireller,that fis, Whetherf' feathering, governing' orv negative pitch. I fi'nthe `gov`erning rangethis lever sets the band zwith-in''virhichjtlieV solenoid` valve M controlsfthe l ieiitiy 'ineither'direction; the pm be int p'a'Sa/g' adnonllt 33. t0 the olfmbel39. This opens" the' `prt" 43` to high rpressure from the line 2l||`driving "thepr'opeller pitch to its extreme inrewsed pitch `or"feathered position. Under these conditions; the oil l from the harnber5i rnay enhaust through the conduit 49,port 4l and port 8 4. vvhiletheoilf'ro'nr the' oer'll 'Arnay exhaust through the ct )r i luit*V 4l,"branch f" and out the loweredge of the alvemernber 30. I n order todecrease the pitch of 'the propeller to such an extentl that goesthrough" Zero pitch to a negative'pitch, and thus' act as an 'air brake,the lever Sjis actuated so as to move the linkage l8 9 to the extremeright; The speed sensitive valve system and pressure from the line 28 isintroduced through the branch n and conduit 4| to the chamber 49 of thevalve 21. Oil is then exhausted from the chamber 39 of this valvethrough conduit 38, branch n and out the upper end of the valve 38. Whenthe piston 44 is forced to its extreme upper position, the port 41 isunmasked and oil under high pressure from the line 24 is introducedthrough the conduit 49to the chamber 5|, and oil is exhaustedfrom thechamber 52 through the conduit 50 and ports 48 and 85 to drain.- Thepropeller blade 5 is thus moved toward decrease pitch until it passes toits extreme position in the negative pitch range. As the blade 5approaches negative pitch, it operates ,a cam 92 beneath the valveplunger 35 so as to shift this valve member to a position connecting thelow pressure line 28 to the passage 36, in readiness for application ofpressure tochamber 39 when the valve member 33 is reset in the speedgoverning position.

The fluid pressure supplied by the system pump and the auxiliary pump 11is normally suicient to accomplish any desired pitch shift of the bladeswhile the propeller is rotating. If, however, yit is not sufficient,such as under conditions when the propeller hasstopped rotating, anelectrically driven pump 92 discharges past a check valve 93 into thepassages 24a and 24. At the end of the branch 24a, there is a movablepiston 94 controlling a drain port 95, and an outlet passage 96 from thepump 92 around the check valve 93. Pump 92 may be driven by anyconventional motor 91. Under normal operating conditions, the pressureinthe conduit 24a pushes the piston 94 upwardly against a spring 98,which connects passage 96 and the exhaust port 95 thus allowing the pump92 to operate against zero pressure. Under conditions of low pressure inthe line 24, the spring 98 will force the valve 94 into the positionshown in Fig. 8, thus closing the port 95. The pump 92 then operatesagainst the check valve 93 to force fluid into the conduit 24a andthence to the high pressure line 24 thus furnishing flow and pressure inthe hydraulic control system.

During feathering or negative pitch operation, the speed responsivevalve unit 29 is by-passed and the control passages 49 and 50 Varesoconnected with the high pressure line 24 and drain line 84 or 85 thatthere is substantially no restriction to the flow of hydraulic fluid tothe ,selected chamber 5| orl 52 for blade actuation '(chamber k52 forfeathering and chamber 5| for negative pitch operation). At the sametime the disconnect relay 562 for the solenoid valve is energized byoperation of the switch 563, thereby disabling the effective operationof the solenoid valve.

Operation draulic chambers 5| and 52.

v Under the second condition of operation, namely, when valve is in thegoverning position and the controlled power plant is off-speed a largeamount, vthe speed responsive valve 29 acts to energize the controlvalve 21, which in turn adjusts the propeller pitch by means. ofservomotor 1pitch control.

having chambers 5| or 52. Under both of these conditions of operation,the valve 21, which is of high capacity, controls the servomotor andacts as a stand-by governor to effect rate of blade angle shifts beyondthe ability of valve I4.

Under the third condition of operation, namely, that of normal governingoperation, more minute adjustments of the propeller pitch are made. Bythe positive overlap of valve 21, the lands 45 and 46 cover the ports 41and 48, respectively, so much that the valve 21 is ineffective tocontrola servomotor under small oir-speed conditions. Theservo-mechanism is then under the sole control 'of the solenoid actuatedvalve I4. The solenoid actuated valve I4 is in the hydraulic systemunder all conditions of operation, but because ofv its smaller capacity,it is ineffective for controlling high rate pitch changes for featheringor reverse The solenoid valve I 4 is controlled by the pulses of currentthrough its windings 62 and 673. These pulses are of lengths determinedby the multi-vibrator circuit included in applicator |69. The length ofthe pulses produced by this multi-vibrator circuit and hence the controlof the valve I4 is determined by three interacting electrical circuits.The main control of this .multi-vibrator is a voltage output of thebridge .circuit |31, primarily responsive to the voltage amplitudeproduced by the three-phase alternator I5, which is directlyproportional to power plant speed and gives the K1 control. The outputof =this bridge circuit is secondarily responsive to the speed voltageadjustment |49 that is controlled by the phase discriminator 24|, andwhose output is a function of the frequency difference between thefrequency of the alternator I5 and a standard frequency source fromelectronic oscillator 240 giving the K3 control. In order to overcomespeed oscillatory characteristicsof high inertia systems, theacceleration or anti-hunt circuit 4| 2 provides an anticipating signalvoltage which is superimposed on the voltage output of the governorbridge circuit I 31 and assists in the control of the multi-vibratorISI-|92 by giving the -Kz f control. The oscillator 249 is synchronizedwith similar oscillators connected at 496, 408 and 4|0. each for one ofthe other power plants desired to be driven in synchronism. Thus, bythese three controls suitable adjustments are made to the solenoidactuated valve i4 to accomplish precise and stable governing of a primemover, as

`well as synchronous operation with similar prime movers.

The present invention is capable of modiication for use as a closedcircuit electro-hydraulic servo system. Such a servo system may be usedas an engine control or for remote actuation of aircraft controlsurfaces and the like. Such a servo mechanism is shown in Figure 13.This system, as illustrated, includes a mechanically unbalancedelectrical bridge I 99| giving position control (K1 control) and amechanically operated Vanti-hunt circuit, which together controlamultivibrator oscillator |003 which in turn energizes a solenoidactuated hydraulic valve |885 through an amplier |064. The solenoidactuated valve |805 controls the hydraulic actuating mechanism I 096 tooperate a bellcrank |940, or any other element to be controlled. Theactuating mechanism I 086 has a mechanical connection through shaft |033to the movable arm I 0 I S of the bridge potentiometer |0|1 and to themovable arm I 829 of the anti-hunt circuit potentiometer |828 to form aclosed servo system. Referring more particularly to Figure 13, thebridge circuit |00| includes `'seriallyconnected 23 a-":"D. C. power"source Iftil, af sensitivity `control potentiometer Ill-I2, a rmanually operablez nr'ibalfencing potentiometer 491.15, `a aser-voloperfated;v relealansing` potentieinet-er"v I Ul'i. When the bridge is'balanced there'is no.: voltage appearing between the movable:Y arms oithe 'potentiometers lith-Sand II'DLII. .'Sincethese arms.are'electrically 'connected to 'fthe points IQ 51 and fm20. lthrou'gh Yresistors I 0`22vand i024, respectively, there isltnen `nofD. vvC.voltage: at' ence. when the bridge is .unbalanced,.ftleerel.apx pearsbetween points i mit and-` IIl.2 ile'aD: C: voltage-'Which isproportional tothe error. "This CD.1"C". voltage, impressed across theseries circuit consi-sting. of resistors H322 to H125, isidividedfvinto1f tWoequal 13.1 C. voltagesv of oppositei'poliarityfwith respect tomid-point I'ilZI. The anti-hunt circuit finc'ludes a'iD. C. power sourceI026,1potentiom veters! t0 28 land i 038-.' resistor w36, capaoitorsi IE132 -and t0'341'and resistors Y i 522 I G23 I=ll2`5f and' |1124.v'Ihef-potentiometer i328 is mechanically adjusted `byltlie servormecnanism follow-up 'shaft della simultaneouslyWith'the adjustment ofthe-poten- .-tiometer |011. The `variable resistorIGH-lisincorporatedto.y controlthe sensitivity *of* the; antihii'ntcircuit. For-a givensetting otpotentiomfeter 403B, the DLC. .voltage dropzthatfappearsacross the resistor i036 is dependent `uponthe 'setti-ng ofpotentiometer H128. UnderstaticvconV fditio'ns'the capacitors i037."Jv'oltage fromy reaching the points I Il I 8 and' H229. *Under"dly-nainic conditions, tnat is, :when the "actuator-i056 is movingfthecontrolled element 'Il040,:and 4therefore vmoving the potentiometer*15028, `-tlne Vvoltageimpressedacrossv the resistor y1* v'I-Il36'isa-.varying voltage. 'Under-these condi'- tions, the capacitors w32:and-|034, ltogether with resistors IGZ 21 tot I2 5- inclusive, vact asan f electrical diierentiating` circuit, r and rantilhunt signalsappearrat the 'points Il!) IEB land IM @with respect to midlpoint IMIwhich` signals are, affdirect -rfunction of the rate oiYK changentposition: of the actuatorrlii. This circuit theref-by `'produces ratesignals-which are superimposed upon`4 the position responsivesignalsproducedl yby bridge I'tI `to give anti-hunt characteristics.These combined signals are: applied? to vthe :grids `:153412 and [864,respectively, off-the multi-vibrator itubesr K543i andA IIB 45 Whosecathodes are connected vvvithpoint 1152i. Thismultievibratorfcifrcuitfis of Conventional design exceptf'torvaria-bleisym- '-xnetry explainedearlier. Voltage fromthe power sourceIMG is impressed across the yresistor 'network including resistorsH248;- I 050i and poten- `Atio'n-ieter- I-l-shunted by resistor H152..Ther-Spoiftenti'ometer 51354 has 1 a Avith fthe@ point l"hence 'theVfrequencyA of oscillation ofathis multivibrator. :The output ofthemultiwibratorf-consis-tsv ofi positive andnegative pulsesshavingrapulselength:ratioiwhichr is a function otbridgeaunbalfance.;and\,ratexofmovement 'of the actuator. *This vsignal is-Limpressed upon the grids,:off-:the am- .,plinertubes m56 and i558, respectivelycto. control:plate-:current in thosev tubes in aratro' egual to '.tiie,pulse-lengthlratio of;y the output signalyof the `multivibrator. -BiasforV the a'mplier-tubestis supplied-from the dropacrossresistoirI'llIB.r,The iD. C; povver.` source H166' furnishes', voltage fop-the amplifiertubes and hence theiygioweri:forA energizing the-solenoid coils I'land-.Iifvrofthevalve w05. The; output signal;v of-,thegtube I 95.6 ist`ti- @lized to .actuaire thel solenoid W63 while the; out.- -putr;oitubef tn isf fused tov 'energize4 the :solenoid .I-(ilIl. i012 isassure-.e of:hvdraulicpressurerand andi i534 block'DJC.

-variable tapfeonnecting If2l for adjusting g11ict.eias.;and

under fpressure xentersthroughnthe Sport. 1I. 'M

Yrestored- 'an'df valve pulsing-at :maybeanyr'suitableilpumpgoficonventionaidesig. 4During1normal'operation ofthefdeviccathefvalve the?conduit.' I'iz .intoifthe-fupper: chamber a'tililizoi .theis'servomotor i086. Theuid-, initnerchamber m89.;.isrizexlriausted?j through.: conduitv I listato idr-ain. W henthe'zsoleno-id; I Bettis @energized'ithe tvalve @plunger |1680 :moves fdownward, ``and .i iiiiid thence through-,tlie conduits' IIl''-intofltlie. cham.-l -ber i082. 5Fl-nidiintheichamber! If'l'B-.isexhausted 4lowf'totne `op,posite:,.sides of l IEISBrduringlithereciprocation of the valve 5103i!vr will' be inaccordance WithA the Vvariable: 'synnnetry of :the operatingmulti-vibrator. The piston Iiliiinreitherrcase isi .moved 'downward orupward, respectively, :at a yratewvhioh' atany instant dependsuponithepulse lengths rat-io of this multi-'vibrator signal. vits Vit `moves itactuatesA shaft w38* to move-v the ilever IlIIliIiftlielcridgepotentiometer-.armtIlIG and-the anti-liuntzvariable resistor arm H129..VThis movement continues untilthe bridge IBM risirebalancedthe-biasfvoltaeesat vpoints A |018 `'and f 1&2@ disappear, themultif-vibratorf-syrnmetry -is 150:50 is resumed. "helabove inventionhasbeen described-specificallylas applied torcertain modi-fieati'onsiorlillustrative purposes oniy. It is intended ithat the invention beconstrued asf` broad'fl'as fcom-pati-ble with @the limitations`con-tained I the? following claims.

yWhat/.is claimed is as follows 1. In apparatusfora'diusting'l-thefpitchfofaircraft lpropeller blades the combinationinclud- Iling; a vhydraulic servornotorffer adjusting the pitcho'f thepropeller blades, a sourcefofhydraulic pressure energized byV 'rotationfof said propeller for furnishing nu-id: under pressure to saidservomotor, ha l'fluid pressurer coi-itrollingA valve: in the rotatingpropeller' and responsive to' the; propeller angularY velocity'Vforgoverning 4lovv of hydraulic fiiiidfromthe source to sai-d`serVornotor,-'a solenoid actuated reciprocating; 'frlui'd' L pressure)controlling: valve connected'` tosaid; source and', havingv a'pair `of'control-,ports connected with opposite.A sides vof said"` servomotor,`means including 'an electronic device 'outside Aof the propeller forcontinuously energizing vsaid solenoid actuated ,reciprocating valveWherebyit effects, pulslel'ike 'r v'now oi' hydraulic, fluid .to 'saidservomotormanual means operatively connected to said vfluid pressuregoverning valve for selectively adjusting the said iluid pressuregoverning valve to a position for governed pitch operation, to apositionfor feather pitch operationY andi to Va' position for "negative 'pitchoperation, isaid' manual means including means operatively connected tovthe fluid'b controlfling valves and ,directive to vary the4 speedsetting Within .the operatingrange at' which the iiuidcontrollingvalvesvvilt govern; 'the now. of; hydranlic.fluid.totheservomotor .during-,governed pitch operation. y

` 2. Speed control apparatus as. claimed-.in claim .1. in 4.the -vmanual control vmeans. includes; l'anV electricfbridec, :means forunna-lansing said bridge, a reversi-blei motor; for adjusting-,tha u-idpressure controllingyval-ves.- andytor rebalancing said.-A electrical;.brides upon ener-,gmation, and', a

.nolerizedirelan sensitive tathenirectionQfmridge

